NGA Articles: The Do-Good Bugs

The Do-Good Bugs (cont)

By: Whitney Cranshaw

Predatory Nematodes

Nematodes, or roundworms, teem in the soil of lawns and gardens everywhere. Some are major plant pests but the great majority feed on soil microorganisms. A few prey on insects, injecting them with lethal bacteria, then feeding on the resultant "goo". Several strains and species of predatory nematodes are produced and sold. Many were originally discovered in soil of the southern United States, although they rarely become abundant even where they are native. Purchased nematodes generally need to be released annually to provide dependable control.

Steinernema carpocapsae is sold under the names BioSafe, BioVector, ScanMask and Exhibit. It is very effective against caterpillars and beetles that live in the soil. This is bad news for beneficial ground beetles but good news if you have problems with cutworms, cucumber beetles, corn rootworm, flea beetles and others. These nematodes also work on raspberry borers, squash borers (inject them into the stems) and peach tree borers (paint them on the trunks). Unfortunately, they don't seem to work as well on thrips, or root maggots and other fly larvae. New techniques of packaging these nematodes mean they can be stored several months at room temperature, which is why they are showing up in garden centers.

Heterorhabditis bacteriophaga works very well on all sorts of white grubs, which are serious lawn pests, as well as on root weevils. But it is more difficult to produce and more perishable, which is why it costs twice as much as Steinernema.

Spined Soldier Bug

Although this beneficial occurs across North America, it isn't commonly found anywhere. Both nymphs and adults feed on caterpillars and the larvae of beetles, including Colorado potato and Mexican bean beetles. They can eat caterpillars that are so big that few other predators can handle them.

Because spined soldier bugs don't exist in high numbers anywhere, you can increase the population near your garden by buying and releasing them. There is only a single supplier of spined soldier bug. There is also a pheromone lure, the Rescue Soldier Bug Attractor, which is a unique product. Most pheromone lures draw only males, so are only good for monitoring insect populations. This one attracts females and is a good way to concentrate wild soldier bugs in your garden.

Trichogramma Wasps

Trichogramma wasps parasitize and kill the eggs of all sorts of caterpillars. So tiny you need a microscope to see them, they occur widely in the United States, especially in the southern half of the country, but are rarely abundant enough to provide much control. They are economical to raise, however, and mass releases can be very effective against corn earworm, cabbageworms, loopers, hornworms, codling moth and other leaf-eating caterpillars. To get the right species of Trichogramma wasps for your climate and pests, discuss your needs with the supplier.

Because it's hard to spot pests' eggs and because Tricho wasps are usually cheap, the best strategy is to plan on weekly or biweekly releases to keep up with new egg laying. Many suppliers are glad to ship on this schedule all season, if you request it. The wasps arrive ready to emerge from eggs of their insectary hosts, which are glued to a card. Prices vary widely, so shop for a good deal.

Trichogramma wasps control the same insects that Bt does. Bt won't hurt the wasps or their developing young, so you can use Bt to kill caterpillars that escape the wasps.

Whitney Cranshaw is an associate professor and extension entomologist at Colorado State University.

Photography by USDA


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